Study contradicts assumptions about hormones and aggressiveness in dogs

Young man with angry black dog on a leash.

We’ve all heard that spaying or neutering your dog (gonadectomy, or removal of the gonads, i.e. the ovaries or testes) will help reduce its aggressiveness. However, a recent study including over 13,000 dogs concluded that this assumption is incorrect.

In the U.S., veterinarians and animal welfare organizations have long supported gonadectomy as a way to reduce pet overpopulation and thereby reduce the number of pets that must be euthanized. Gonadectomy greatly reduces the presence of sex hormones, resulting in infertility.  It has also been used to treat or prevent behavior problems, such as aggressiveness, in dogs.

Over the past few decades, a growing number of people have questioned the impact of this practice on long-term health. Research has revealed some surprising findings — such as that health problems including cancer, autoimmune disorders, incontinence, and orthopedic conditions are more prevalent in dogs lacking natural hormones.

Now, a study published in Frontiers in Veterinary Science has found that gonadectomy is not related to a dog’s level of aggression toward familiar people or dogs. Spayed and neutered dogs — specifically those that had surgery at the age of 7-12 months — actually exhibited a higher level of moderate to severe aggression towards strangers. These results add to already increasing evidence that removing the influence of sex hormones may not always have the expected impact in dogs (and that the breed and sex of the dog and the timing of gonadectomy affect outcomes too).

As we learn more about the negative health consequences of gonadectomy, many dog lovers are looking for alternatives for Fido. Fortunately, hormone-sparing alternatives exist that preserve natural sex hormones but sterilize the dog. For more information, take a look at our page on hormone-sparing sterilization methods, and our list of veterinary practitioners who offer such alternatives.

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